290 PHYSIOLOGY. 



may be obtained. The graphic record, or pulse-tracing, is known as 

 the sphygmogram. 



A sphygmogram is a graphic representation of the variations of 

 pressure inside an artery. 



The main features of the sphygmographic record are an abrupt 

 ascent with a descent that is more gradual and wavy, representing the 

 rise and fall in pressure due to ventricular systole and diastole. The 

 wavy appearance of the downstroke is due to the elastic recoil being 



Fig. 93. Dudgeon's Sphygmograph. (LAHOUSSE.) 



more constant and of longer duration than the ventricular systole. 

 The sudden upstroke represents very forcibly the sudden influx of 

 blood into the aorta during systole, while the more gradual down- 

 stroke represents the slower fall of arterial pressure during diastole. 



The line of ascent represents the dilatation of the artery by ven- 

 tricular systole when the semilunar valves are forced open and the 

 contents are projected into the artery. The top of the primary wave 

 is pointed normally ; so has received the term apex. 



As a rule, the ascent of the pulse-curve is nearly vertical. When 

 a series of closely-placed elastic vibrations occur in the upper part of 

 the line of ascent so that the apex appears dentate and forms an angle 

 with the line of ascent, then the sphygmogram becomes anacrotic. 



